This disclosure relates to a method for removing oxide from a turbine component, and more particularly, for removing oxide formed in cracks of the turbine component.
Metal alloys are often used in industrial environments, which include extreme operating conditions. As an example, gas turbine engines are often subjected to repeated thermal cycling during operation. The standard operating temperature of turbine engines continues to be increased, to achieve improved fuel efficiency. The turbine engine components (and other industrial parts) are often formed of superalloys, which can withstand a variety of extreme operating conditions.
In addition, turbine components, e.g., gas turbine airfoils, can develop cracks. During service, these cracks are often exposed to oxidizing conditions. Under such conditions, which often include temperatures in the range of about 1400–2100° F. (about 760–1149° C.), various oxidized products (mainly thermally-grown oxide or “TGO”) are formed on and within the cracks.
When turbine engine components are overhauled, the cracks are repaired. A conventional method for repairing these cracks is a brazing procedure known as Activated Diffusion Healing (“ADH”). However, in order to perform this repair procedure, the oxide in the crack must be completely removed since oxides, in particular aluminum, titanium, and chromium oxides, prevent wetting of the alloy surface by the braze material.
The conventional method for cleaning the oxide from the cracks is known as “fluoride ion cleaning” (“FIC”), which is a high temperature gas-phase treatment of the component with hydrogen fluoride and hydrogen gas. The FIC method has certain drawbacks because the equipment is expensive to purchase, operate, and maintain. In addition, hydrogen fluoride is a hazardous chemical and thus, it is desirable to develop an alternative method for cleaning oxide from the cracks in gas turbine airfoils.